A dictionary does not help us. Truth is "the quality or state of being true" (ODCE). From which we can assume that falsehood is the quality or state of not being true. A first definition of truth is therefore the sum total of all true or false propositions in our language. But that does not seem to fit either of Jesus' statements about truth or Pilate's question.
Among the many true or false propositions in our language The Oxford Dictionary of Current English Usage tells us that the quality or state of being true can refer to being :
1. In accordance with fact or reality
2. Genuine; rightly or strictly so called
4. Accurately conforming to (a type or standard)
5. Correctly positioned or balanced; upright, level
6. Exact, accurate (a true copy).
So we wonder how Pilate was using the word truth (alytheia) when he asked his question? A New Testament Greek Lexicon says the word often means truthfulness, which is the same as our English "quality or state of being true." Then it adds dependability and uprightness, which includes our English meanings 3, 4, & 5. The idea of reality (as opposed to mere appearance) appears as our common English meaning 1. There are also many uses of the term "The truth" among early Christian writers to describe the content of Christianity as absolute truth. That is not common usage in English, though it is bandied about without any clear explanation in some Christian circles.
In our post-modern situation it has become obvious that the propositions "That's true" and "That false" do not belong to one universal system of truth. What is true in Base 2 mathematics is not at all true in Base 10. What is true in Newton's system is often false in Einstein's relativity. You have to know what system a speaker or writer is working in. If a child says "That's my bear" it could be a true fact in terms of ownership, and you don't say "That's not a bear" because it does not conform to zoological reality." "That's a Van Gogh" could be false because the original was painted by Matisse. It could also be true that it is a Van Gogh, but it is not true that the painting is an original.
Clearly truth and falsehood only makes sense in an agreed system for evaluating what is true. There are true and false propositions in astrology, but astronomers have no way of proving or disproving whether the stars influence what will happen to us.
Pilate was certainly familiar with different systems of truth among the Stoics and Epicureans of the Greek world. In Jerusalem he could also distinguish Pharisee truth from Sadducee truth, and the religion of the Essenes from the Zealots. So his rhetorical question "What is truth" (John 18:38) really expressed the idea that "I am a Roman governor charged with keeping all these different sects under control, and I cannot judge between them and you on that basis." In that sense he was making a post-modern statement about being unable to settle among alternative religions and ideologies.
How then do we take Jesus' words "Everyone who belongs to the truth listens to my voice" (John 18:37)? This is not the truth of the different systems of truth that Pilate had encountered. Nor is it one universal truth, of which each system of truth is an imperfect part. This is the truth concerning the origin, outworking, and end of the Kingdom, which Jesus had revealed in his life and teaching (John 18:36). Aspects of that truth are set out for us in the parables and dozens of metaphors in the Gospels.
What then did Jesus mean the night before when he said to his inner circle of disciples "I am the way, and the truth, and the life. No one comes to the Father but by me" (John 14:6)? There is very little in the other Gospels about the way we will move from this life through the resurrection to the perfection of the Father's heaven. But in John's Gospel at the last supper Jesus claims to be one who opens up the way by his death, resurrection and ascension. He is the key and the heart of the truth that was never known till he came (John 1:10-18, Colossians 1:13-20, Hebrews 1:1-4, 1 John 1:1-2). His life on earth was totally energized by the Spirit, and he imparts that life to us by the same Spirit.
The truth of the Kingdom therefore includes all that Jesus gave us in the parables and metaphors of the Synoptic Gospels. In John's Gospel it also includes the way, the truth, and the life that take us through our own death and resurrection. None of those truths can be arrived at from first principles, or some grasp of absolute truth, nor can they be proved by some deductive logic. They can only make sense to those who are taught by the Holy Spirit of God (1 Corinthians 2:1-13).
Some think "No one comes to the Father except through me" is meant to inform us that only those who get to hear about him, and make a decision to accept him as their personal Saviour will make it to heaven. But the text does not say that..
He is the way, the truth, and the life not only for those who understand, but also for infants, retarded persons, and the ignorant and wrongly taught among all nations. We and they can only be saved by the unmerited grace of the Son of God. We should not add that we have to do anything for him to perfect us. And thankfully we are not saved by understanding how we are saved, or by our devotion, least of all our obedience: otherwise none of us would make it. He can even save those who have a wrong explanation of who God is. In The Great Battle C.S.Lewis pictures Aslan's welcome of the fellow who had spent his life fighting for the god Tash. What counted was that his heart was really longing for what Aslan turned out to be when he finally met him.
If I have grasped the language games for "truth" in the words of Pilate and Jesus, then we have a post-modern impossibility of proving the truth of one religion or another. In that sense Pilate was right. God does not use human wisdom, intelligence or logic to force us into the Kingdom.
We are saved by grace alone and by his truth alone (John 1:14, Ephesians
2:8-10). But if the Spirit is working in us we will begin to understand
what the Messiah is doing in us and for us. And when that happens we soon
know that no other religion or ideology is able to reveal the love of God
to us, perfect us in love, or take us through death to a glorious resurrection.
The experience of suddenly being enlightened, often called conversion,occurs when when someone has lived indoors with the drapes tightly shut for a long time suddenly draws the drapes and ventures into the sunshine. It is a great moment, but the sunshine was ours already. Little children enjoy the sunshine of God's love, and it is often in their teens under peer pressure that they decide to shut the free grace of God out.